public class HomeWork07{
	public static void main(String[] args) {
		double sum = 0;
		for ( int i = 1; i <= 100; i++ ) {
			if(i % 2 == 0){
				sum = sum - 1.0 / i;
			}else{
				sum = sum + 1.0 / i;
			}
		}
		System.out.println(sum);
	}
}
	
